Photographic processes



United States Patent 3,155,507 PHQTQGRAPHIC PRUQESSES Ralph Kingsley lllalre, Westiield, N..l., assignor to E. l. du Pont de Nemours and Company, Wilmington, Beth, a corporation of Delaware No Drawing. Filed Nov. 8, i962, Ser. No. 236,420 21 Claims. (Cl. 96-64) This invention relates to photography, and more particularly to new photographic processes useful therein.

The principal processes of photography are based on the use of colloid-silver halide emulsion layers. In the prior art processes a latent image is formed by imagewise exposure of a radiation-sensitive silver halide emul sion layer. Silver halide bearing a latent image has been developed to silver by selective reduction in these instances.

In the prior processes of photography the unreduced silver remaining after development has been removed by silver halide solvent or rendered insensitive or transparent by treatment with complexing agents. Optional after-treatments include intensification and reduction, toning and tinting. However, the primary or first step in image formation always has been based on the selective reduction step.

It is an object of this invention to provide new and versatile processes for forming silver and other images.

Another object is to provide novel processes for pro ducing photographic images that do not depend on conventional selective reduction of exposed silver salt images. A further object is to provide such processes which are simple, dependable and give results equal or superior in quality to the prior conventional processes. A further object is to provide new and more sensitive processes for producing direct positive images. Still further objects will be apparent from the following description of the invention.

The process of the invention comprises:

(a) Exposing, imagewise, to actinic radiation, a photographic element containing silver halide crystals previously made relatively less soluble in a silver halide solvent by treatment with an organic compound capable of forming a silver salt and whose silver salt is of lower solubility in water than silver chloride, and

(b) Treating said element with an aqueous solution of a silver halide solvent, ellecting solubilization of the silver halide in the more exposed areas at a rate substantially greater than in the less exposed areas until a positive image comprised of silver halide is produced; said organic compound being characterized in that when admixed with an aqueous silver halide dispersion it protects the silver halide grains to such an extent that when a silver halide dispersion protected by said compound is treated with 10% (by weight) aqueous sodium thiosulfate, at least three times the amount of silver halide remains undissolved as in a similar dispersion successively treated with 5% aqueous sodium hypochlorite and 1 3% aqueous sodium thiosulfate, after vigorous agitation of the dispersions for 30 seconds at 25 C. The dispersion so successively treated clears whereas the other dispersion remains turbid. The selected organic compound may be further characterized as being a compound whose silver salt is less soluble in water than silver chloride crystals. The treated residual silver halide image may then be converted to metallic silver, dyed or toned images. The solvent for the silver halide layer is an aqueous solution of a silver halide solvent, e.g., sodium thiosulfate.

The novel compositions useful in the process of the invention are dispersions of emulsions of specifically treated light-sensitive silver halide grains in a Water-permeable organic colloid and they are prepared by admixing with 3,1555%? Patented Nov. 3, i964 the silver halide before or after precipitation, an organic compound of the foregoing kind. The compound can be added to the aqueous colloid silver halide emulsion prior to coating onto a suitable support or by bathing or impregnating the emulsion layer with a solution, e.g., an aqueous alcoholic solution of the compound. In the working examples below, the amount of organic compound in the silver halide emulsion is from 0.125 to 314 g. per mole of silver halide but wider ranges of concentration can be useful, depending upon the particular organic compound, the size .and nature of the silver halide crystals, the presence of other materials which may partially cover the surface of the silver halide crystal, and upon various other factors.

The gelatinzsilver halide ratio is quite flexible and may vary from 3:1 to 1:30 depending on the particular organic compound and application.

In one commercially practical aspect of the invention, the silver halide is present in much higher concentration than in conventional emulsions and emulsion layers.

In an important image-forming aspect of the invention, direct positive images are formed by a process which comprises (a) Exposing, imagewise, to :actinic radiation a photosensitive layer oomprising silver halide crystals treated with the organic compound as described above,

(b) Treating the exposed layer in a solution of a silver halide solvent to remove soluble silver halide in the exposed image areas, thus forming a positive silver halide image, and

(0) Washing the resulting layers.

If desired, the silver halide image may be viewed directly, e.g., by projeeton (if on a transparent support) or it may be intensified by (d) Converting the residual silver halide to silver by treatment in a fogging developer, e.g., a high pH, 1- phenyl 4 methyl 3 pyrazolidone/hydroquinone developer containing iodide ion or by fogging the emulsion by exposure to light and then treating with a silver halide reducing agent, e.g., a conventional silver halide developer, and

(2) Washing the developed layer to reveal a positive silver image in the original non-exposed areas.

The imagewise solution of the exposed silver halide/ organic compound stratum may be effected by the silver halide solvents commonly used as photographic fixing agents, e.g., sodium thiosulfate, sodium thiocyanate, concentrated solutions of potassium bromide, etc. Reduction of the treated, residual silver halide may be accomplished by use of any chemical reducing agent oapa ble of reducing silver ion to silver metal, e.g., hydroquinone, metol, sodium hydrosulfite and stann ous chlo-- The present invention embodies a broad new photographic process and is not limited to a narrow class of organic compounds with which the silver halide crystals may be treated in carrying out the invention. Instead, a large number of compounds can be used and their utility can be readily determined by a relatively simple test. Essentially, the test consists of two separate steps, which will be designated Test A and Test B. In Test A,

the candidate organic compound must render a dispersion of silver halide crystals insoluble in a silver halide solvent, i.e., an aqueous solution of sodium thiosulfate, at some pH between 1 and 13. If the candidate compound meets the insolubility requirements of Test A, it must also meet the requirements of Test B by forming with said dispersion of silver halide crystals a reaction product which, upon treatment with an aqueous solution of sodium hypochlorite, becomes soluble when subsequently treated with aqueous sodium thiosulfate. The following practical tests are provided in further exemplification of the invention and include specific concentrations of solutions, times, etc., so that the utility of organic compounds may be readily and positively identified.

TEST A A solution nearly saturated at 25 C. with a candidate organic compound is prepared using ethanol, acetone, dimethyl formamide, water or other suitable solvents. Depending on the solubility, a solution concentration from 0.01 to 10 percent by weight is obtained. Twentyfive ml. of a silver chlorobromide dispersion containing 25 mg. of silver halide (calculated as silver bromide), prepared as described below, is treated with small increments (i.e., about 0.1 to 0.2 ml. at a time) of the said candidate solution under safelight conditions (Wratten 1-A filter or equivalent) until the silver halide dispersion either is rendered insoluble in 10% aqueous sodium thiosulfate or the candidate is found not to cause insolubilization. Generally insolubilization will occur upon the addition of 0.05 g. or less of said candidate compound, calculated as the pure compound. Compounds which must be used in substantially greater quantities than this, e.g., 1-2 g. to effect insolubilization are considered less preferred compounds. The silver halide dispersion insolubility is determined by taking a 0.5-ml. portion of the silver halide dispersion (after each incremental addition of the candidate organic compound), adding about 0.1 to 0.2 ml. of 10% aqueous sodium thiosulfate solution and observing the turbidity after 30 seconds.

As a control, one should use 25 ml. of water to which small increments of the candidate solution are added. Half-milliliter portions of the control are treated in the same manner with the sodium thiosulfate solution. The presence of visual turbidity relative to the control is sufiicient to satisfy the definition of insolubility in this test.

This test may be repeated for various pH increments from 1 to 13. Although there is some optimum pH value at which the test is most sensitive, this is not a sharp maximum which must be precisely attained. Rather, it has been found that there is a fairly broad range of pH values (e.g., 2.0 to 3.0 pH units) over which the test has a satisfactory sensitivity. In practice, the silver halide dispersion might be tested without adjustment (e.g., at pH 5.0 to 7.0) and if insolubilization occurs here, Test A is completed. If there is no insolubilization, the tests is repeated at a higher pH (e.g., about pH 11-13). If there is still no insolubilization, the test is conducted with emulsion adjusted to a lower pH (e.g., about pH 1-3). Thus three different pH values represent a practical maximum number which must be investigated to determine whether or not insolubilization will occur.

TEST B An organic compound capable of insolubilizing a silver halide dispersion according to Test A is now ready for the next test, which again will be conducted under safelight conditions. To the above silver halide dispersion, there is added the minimum amount of a solution of the candidate organic compound found necessary for insolubilization. Half-milliliter samples of the dispersion are placed in two test tubes. To one sample is added 0.5 ml. of water; to the other is added 0.5 ml. of a to 5.5% by weight aqueous solution of sodium hypochlorite. Next, there is added to both samples, 1.0 m1. of

an aqueous 10% by weight solution of sodium thiosulfate. If, after standing for up to 30 seconds, the sample treated with sodium hypochlorite clarifies (or becomes less turbid) relative to the control sample, the candidate organic compound meets the requirements of Test B and is satisfactory for use in accordance with the invention.

Silver Halide Dispersion Preparali0nDispersi0rz l The silver halide dispersion disclosed in Tests A and B is prepared according to the following specifications. In red light, 30 g. of photographic grade gelatin is soaked in 1100 ml. of distilled water for 10 minutes. The temperature is then raised to 120 F. and g. of solid ammonium chloride added. The mixture is stirred at F. and after the ammonium chloride is completely dissolved, a solution made by diluting 500 ml. of 3 N silver nitrate with 2000 ml. of distilled water is added while stirring the solution for 5 seconds. This mixture is held at 120 F. for 4 minutes with stirring, and then ml. of 3 N ammonium bromide are added (30 mole percent) in 10 seconds. The mixture is held an additional 15 minutes at 120 F. with stirring and then cooled to 100 F. A mixture of 75 g. of the sodium salt of technical lauryl alcohol sulfate (a white powder) and 7 ml. of 3 N sulfuric acid is added in 10 seconds to the silver chlorobromide, stirring continued for one minute and then the mixture allowed to settle. The supernatant liquid is decanted and replaced by 2000 ml. of distilled water containing 4 g. of sodium chloride. This mixture is stirred for 5 minutes at 100 F., allowed to settle and decanted again. Two hundred ml. of distilled water is added to the silver halide curds and the temperature adjusted to 95 F. This mixture is vigorously stirred for 10 minutes at 95 F. and then the pH is adjusted to 6.1101 with aqueous sodium hydroxide solution. The redispersed emulsion is then analyzed for silver halide content calculated as silver bromide and a dispersion is made by diluting the appropriate amount with distilled water such that the dispersion contains 1 mg. calculated silver bromide per ml.

Organic compounds useful in this invention, by being capable of passing both the insolubilization and the solubilization tests above (Test A and Test B, respectively), may be found among a wide variety of organic classes. The true scope of the process of this invention can only be identified according to the above tests. However, it appears that most suitable organic compounds have at least one form which can be represented by the general formula wherein X is an atom capable of forming a silver salt by replacement of the hydrogen atom and R is an organic radical having a carbon atom linked directly to X. Tautomeric forms of the compound may result in different linkages for the hydrogen atom than shown in the formula. X is preferably an atom selected from sulfur, selenium and nitrogen according to the examples below. The scope of this invention, however, comprehends any organic compound which successfully passes screening Tests A and B.

Particularly preferred organic compounds of the formula R-X-H are those which form silver salts of the formula Among the useful silver salts of the above formula are those which are insoluble in aqueous ammonium hydroxide at pH 12.

Dispersed crystals of silver halide, treated with an appropriate amount of a suitable organic compound are affected by exposure of a portion of said crystals to actinic radiation, e.g., ultraviolet, visible, infrared, X-radiation, etc, to such an extent that at least 20% of the less soluble crystals remain when 90% of the more soluble crystals dissolve when treated in 10% by weight aqueous sodium thiosulfate solution. Useful organic compounds in which in the above formula represents the sulfur atom include mercaptans and their tautomers and especially the mercaptothiazoles, mercaptotriazoles and mercaptotetrazoles which are devoid of solub lizing groups. Generally, the presence of solubilizing groups should be avoided in order that reaction products with silver halide will be formed which will significantly reduce the solubility of silver halide grains in silver halide solvents. There are exceptions to this rule, particularly in the case of suitable compounds containing solubilizing groups which are compensated for by the presence of insolubilizing groups, e.g., long chain alkyl groups. Suitable specific compounds from these classes include those disclosed in Chilton et al. US. Patent 2,432,506. Other useful compounds include mercapto-oxazoles, naphthalene thiols, phenanthrene thiols and anthracene thiols. Since selenium is chemically so closely related to sulfur, it is obvious that many compounds are suitable in which sulfur is replaced by selenium. Also, as shown in the examples below, certain compounds, in which X of the formula represents the nitrogen atom, have been found to give excellent results. The symbol X might represent other atoms, so long as the organic compound in question fulfills the conditions prescribed by Test A and Test B above. The chemical testing for selecting suitable compounds has been found to give absolute correlation, i.e., organic compounds which have been subjected to the pair of tests have produced without exception when tested in actual photographic emulsions, the very effects predicted by said tests. Combinations of the compounds with various basic dyes, e.g., dyes of the cyanine class and Methylene Blue (Colour Index No. 922), Crystal Violet A0 (Colour Index No. 681) and Rhodamine 6 GDN Extra (Colour Index No. 752) have proven useful additions.

The silver halide need not be a combination of silver chloride and silver bromide, but may be silver chloride, silver bromide and other mixed halide systems conventional in photographic practice, e.g., silver bromoiodide. While, for rapid processing, a high silver halide to binder ratio is preferred as described in several of the examples, more conventional ratios can also be used.

In place of part of the gelatin, other natural or synthetic water-permeable organic colloid binding agents can be used and in some cases such binders can be used alone. Such agents include water-permeable, or water-soluble polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, ethers and acctals having a large number of intralinear CH CHOH groups, hydrolyzed interpolymers of vinyl acetate and unsaturated addition polymerizable compounds such as maleic anhydride, acrylic and methacrylic acid esters and styrene. Suitable such colloids of the last-mentioned type were disclosed in US. Patents 2,276,322; 2,276,323 and 2,397,866. The useful polyvinyl acetals include polyvinyl acetaldehyde acetal, polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents which can be used include the poly-N- vinyllactams of Bolton U.S. Patent 2,495,918, various polysaccharides, e.g., dextran, dextrin, etc., the hydrophilic copolymers in Shacklett U.S. Patent 2,833,650, hydrophilic cellulose ethers and esters, and polymers of acrylic and methacrylic esters and amides. It has been found practical to treat silver halide layers on a base material in the essential absence of a binder, e.g., by chemical or vacuum deposition.

The emulsions may optionally contain any of the usual adjuvants customarily employed in silver halide systems so long as they do not interfere with the adsorption and complexing action of the essential ingredient of the invention.

The emulsion can be coated on any suitable support, e.g., cellulose esters, cellulose mixed esters; superpolymers, e.g., polyvinyl chloride (co) vinyl acetate, polyvinyl acetals, butyrals; polystyrene; polyamides, e.g., polyhexamethylene adipamide, polyesters, e.g., polycarbonates, polyethylene terephthalate, polyethylene terephthalate/ isophthalate, esters formed by condensing terephthalic acid and its derivatives, e.g., dimethyl terephthalatewith propylene glycol, diethylene glycol, tetramethylene glycol, cyclohexane-1,4-dimethanol (hexahydro p xylene dialcohol); paper, metal, glass, etc.

As disclosed earlier, the desirable concentration of the selected organic compound depends on many factors such as the size and solubility of the organic compound, the nature of its reaction with silver halide, the size and nature of the silver halide crystals, the presence of other. materials which may react with or be adsorbed to the surface of the silver halide,.etc. In Example VI below, a large number of organic compounds are disclosed which were tested in a dispersion of silver halide crystals wherein the average grain size was 0.35 4 (micron) in diameter, therefore about 0.043u in volume, assuming cubic grains. The silver halide comprised 70 mole percent silver chloride and 30 mole percent silver bromide, with a specific density of about 5.7 g./cc. or 5.7 10- g./ The weight per individual crystal or grain is Assuming a molecular weight of 157 for the mixed AgCl-AgBr crystals, and dividing this number by the weight per grain, gives 157 g./mole:-0.25 10* g.=6.3 x10 grains /mole.

The area of a cubic grain of 0.35 diameter=6 .35 =.74,u

which, multiplied by the 6.3 x10 grains per mole, gives a molar surface area of 4.6X10 u or 4.6)(10 square angstroms.

A particularly preferred organic compound is 2-mercapto-4-phenylthiazole (hereinafter to be referred to as MPTU. Assuming that a single molecule of MPT could occupy an area of 28 square angstroms, it would require 1.5 10 molecules to occupy a molar surface area or" silver halide. With a molecular weight of 193, this would require to just cover the surface of one mole of the silver halide crystals. In Example VI it required 1.2 l0- g. of MP1 to insolubilize 2.5 l0- g. of silver halide of average molecular Weight 157. Therefore according to experimental data (test tube results) it would require of MPT to insolubilize one mole of the silver halide. More significantly, as disclosed in Example XII in a photographic emulsion coated on a film base support, it was found that 0.4 g. of MPT per mole of silver halide gave optimum results. This compares more closely with the theoretically determined amount of MPT required to cover the silver halide surface.

As shown in various examples below, e.g., Example I, elements suitable for this novel process can be prepared by bathing a photographic film in a solution of an appropriate organic compound. In this embodiment, the silver halide crystals near the surface of the coated emulsion stratum are in contact with a higher concentration of the organic compound. Crystals farther from the surface, are treated with less of the organic compound and, if the rate of diffusion is sufiiciently slow, there may be considerably less of the organic compound (even approaching zero) reacting with the lower than with the surface silver halide crystals. In such elements, satisfactory results might be obtained with only a fraction, e.g., onehalf, of the amount of the organic compound theoretically calculated as required to just cover the surface of a mole of the silver halide crystals.

193x =0.4s g.

A further aspect of the invention relates to a process of preparing photographic emulsions useful in the process. This process comprises (1) Preparing a photographic silver halide emulsion having a pH at which the silver halide crystals are rendered less soluble in a silver halide solvent by treatment with an organic compound characterized as set forth in column 1 and being capable of forming a silver salt and whose silver salt is of lower solubility than silver chloride in water, and

(2) Admixing therewith such an organic compound. By correlating the pH of the emulsion with the insolubilization characteristics discussed above, a novel process for ma 'ing photographic emulsions of unique light response is attained.

The organic compound is present in the emulsions of this invention greater than fog inhibiting amounts, the later amounts being the maximum quantity vhich provides low fog without serious loss in speed.

The invention will be further illustrated by but is not intended to be limited to the following examples.

EXAMPLE I A photographic element was prepared by coating an aqueous gelatin dispersion of silver chlorobromide (70 mole percent silver chloride and 30 mole percent silver bromide) on a film base prepared as described in Example IV of Alles US. Patent 2,779,684. The dispersion had a ratio of silver halide to gelatin of 28:1 by weight and was coated at a pH of 6 at a rate of 116 milligrams of silver halide per square decimeter. After drying, the element was bathed for about 30 seconds in an ethanol-water solution of Z-mercapto-4-phenylthiazole having a pH of 5.1 and dried. The solution of 2-mercapto-4-phenylthiazole was prepared by diluting 5 ml. of a stock solution (1 gram of the compound made up to 100 ml. in ethanol) with an additional 20 ml. of ethanol and ml. of water. The dried element was then exposed behind a photographic transparency for seconds to the radiation from a General Electric Z-A photofiood lamp at a distance of about 6-10 inches. The exposed element was then immersed in a 12.8% aqueous solution of sodium thiosulfate for seconds resulting in removal of the silver salt in the exposed areas. Subsequently, the fixed film was then rinsed briefly in water and bathed in a rapid acting fogging photographic developer solution comprising 1-phenyl-4- methyl-3-pyrazolidone and hydroquinone as reducing agents to which there had been added potassium iodide and a direct positive image formed. All of the above operations were carried out in ordinary fluorescent room illumination.

Where a more sensitive product is prepared by appropriate selection of such factors as grain size, silver halide composition, etc., it may be desirable to use conventional photographic darkroom handling of the element prior to the image exposure. During the developing step, the treated element is converted into an exact reproduction (i.e., direct positive image) of the original transparency. After brief washing in water and drying, it is satisfactory for use in any application where an exact reproduction is desired, e.g., in the graphic arts field, for a projection transparency, etc.

EXAMPLE 11 Example I was repeated except that l-phenyl-S-mercaptotetrazole was substituted for the 2-mercapto-4- phenylthiazole of that example. The pH of the treating solution was 3.5. The results were similar to those obtained with Example I.

EXAMPLE III Example I was repeated except that Z-naphthalene thiol was used in place of the Z-mercapto-4-phenylthiazole of that example. The pH of the treating solution in this case was 5.65. The results were similar to those obtained in Example I with a direct positive image being obtained.

EXAMPLE IV Example I was repeated except that Z-mercaptobenzoxazole was used in place of the 2-rnercapto-4-phenylthiazole of that example and the pH of the treating solution was adjusted to 11.55 with aqueous 0.1 molar sodium carbonate before being made up to final volume with water. As in Example I, a direct positive image was obtained.

EXAMPLE V A photographic element was prepared by coating an aqueous gelatin dispersion of silver bromoiodide (93.86 mole percent silver bromide and 1.14 mole percent silver iodide) on a cellulose acetate film base and drying the coating. The dispersion had a ratio of silver halide to gelatin of 1.00:1.03 by weight and was coated at a pH of 6.2 at a rate or" milligrams of silver halide -er square decimeter. After drying, the element was athed for 30 seconds in a dilute aqueous solution of L-mercapto-4-phenylthiazole and dried. The solution of IZ-mercapto-4-phenylthiazole was prepared by diluting 5 ml. of the stock solution used in Example I with 10 ml. of ethanol and 20 ml. of water, and had a pH of 4.60. The element was exposed as in Example 1 except that the exposure time was increased to 30 seconds. It was then bathed in the sodium thiosulfate solution of that example for 60 seconds, rinsed briefly in water, bathed in the same developer for 60 seconds, all operations being carried out in ordinary fluorescent room illumination. A direct positive image was formed in the same manner as in Example I. The same course of treatment applied to a commercial panciiromaticallysensitized emulsion gave comparable results.

In connection with the above examples, it has been found that the pH. of the treating solution used to initially bathe the film has a striking effect. With very low pH the effect of the treatment is minimized or completely eliminated. For example, with the compound of Example I the elfect of the treatment can be eliminated if the treating solution has a pH ca. 1 or lower. While all of the compounds produce desirable results over a wide pH range, each compound apparently has an optimum pH range which is most elfective. It will be apparent to one skilled in the art that simple tests can be run to establish the best pH conditions for operation.

EXAMPLE VI Tests A and B have been described earlier as procedures whereby one can determine whether or not a given organic compound is suitable for use according to the process of this invention. Many of the compounds which were indicated as suitable according to the screenmg procedures of both tests, have been incorporated into actual photographic coatings and good results have been obtained. Below there are listed a great many organic compounds which were tested in this manner including a few of the compounds which have been found to be inoperable. Of the unsuitable compounds shown, most failed to produce the insoluhilty required of Test A and were therefore not subjected to furthe testing. One of the nitrogen-containing compounds, 3-methyl-4-(m-nitrophenyl)-5-pyrazolone, produced the required insoluoility of Test A but failed to meet the requirements of solubilization according to Test B. Since it was impracticable to perform complete photographic experiments with each and every compound screened according to Tests A and B, a simulated photographic test was devised and will be designated as Test C. It is noted that there is complete testing correlation in that any compound which was found suitable according to the photographic test to be described in the next paragraph was also found suitable according to Tests A and B.

TEST C A 0.5 ml. portion of the lnsolubilizcd dispersion prepared 1n Test A under safelight conditions is placed in a 12 x 75 mm. Pyrex test tube three inches from a No. 2 refiectofiood lamp. This insolubilized dispersion is exposed to the lamp for up to 10 minutes. A control consisting of another 0.5 ml. portion of the insolubilized silver halide dispersion from Test A is taken under safelight conditions. Two-tenths of a milliliter of 10% aqueous sodium thiosulfate is added to each of the dispersion samples taken and compared under safelight conditions. Any reduction in turbidity of the dispersion exposed to the reflectofiood lamp compared to the unexposed control after treatment with aqueous sodium thio sulfate solution shows that photosulbilization occurs.

Tests A, B and C Were all conducted using Silver Halide Dispersion I, the preparation of which Was given immediately following the description of the procedure for Test B. To determine an approximate minimum concentration of the organic compound required to effect insolubilization of silver halide in the presence of an aqueous solution of sodium thiosulfate, the qualitative procedure of Test A was repeated in a more quantitative manner, using a ripened, Washed and redispersed (but not chemically sensitized) gelatino-silver chlorohromide emulsion as described in Example I of assignees ccpending application, Nottorf, U.S. Serial No. 94,989, filed March 13, 1961. This emulsion is designated in the table below as, Dispersion II.

THIOUREA DERIVATIVES Test Results with Dispersion I Gms. Compound to Insolubilize Compound Insolubilizatlon Test A Dispersion II Containing 25 mg. Silver Halide Chemical Solubilization Test B Photosolubilization Test C Thioocetanilid e Thiobenzanilide.

Thionrea N-ph enylthiouree l-(l-naphthyl) -2thiourea 1, l-diph enyl-Z-thionreal-ethyl-l-(l-naphtliyl) -2-thi0urea 1,3-di-n-butyl-2-thiourea 1-ethy1-3-phenyl-2-thiourca Thiocarbanilide-- .2,2'-diethylthiocar nilide 12. 1,3-dibenzyl-2-thi0urei 1,3-di-(1 naphthy1)-2-thi0urea. Thiosemicarbazidp 4-phenyl-3-t-hiosemicarbazidel,5-diphenyl-3-thi0carboliydrazide. Diphcnylthiocarbazone a-Mercapto acetanilide" 1,3-diallyl-2-thiourea.

. 1-allyl-3-phenyl-2-thiourea.

21. 1,3-di-n-oetyl-2-thiourca Thioacetamide l-acetyl-Z-thiourea 1. 2-mercapto-4-phenyltliiazole Insoluble 0.00012 2. 2-mercaptobenzothiazole 0.00008 3. ti-amino-2-mercaptobenzothiezole 0. 0014 4. G-nitm-Z-mercaptobenzothiaz'fle (10014 5. 1-phenyl-5-mercaptotetrazole (M109 6. 5-(2-hydroxybenzylidene)-2-thiohydanto1n- 0.0075 7. 2-mercaptobem 0.02 8. 2-mereapto-5 aminob 0.006 9. 2-mereapto-5-nitrob imid'wole 0.0012 10. Z-mercaptoben n ole 0.0003 11. 2-mereapto quinoline.. 0.002 12. 2-naphth0(l,2)-thi zolethiol 0. 004 13. Phenyl biquanidc mercapto benzothiazole. 0. 0001 14. 2-mercapto-5,G-dimethoxybenzo 0.015 15. fi-acetylamino-fZ-mercapto benzothiaznle 0.03 16. fi-isobutyrylarnino-21nercaptobenzothiaznle 0, 0003 17. fi-n-octan0ylamino-2-mercaptobenzo 0. 0003 18. G-lauroylamino-2-mereaptobcnzothiazole 0.002 19. 4-phenyl-1,3,4-thiadiazolidenc-2-thi0ne 0. 0002 5,6-dil1ydro-4-phenyl-4H-1,3,4-thiadiazi.ne-2-thiol 21. 2-thiozolidinethinne 22. Rhodanine. 23. l-acetyl-2-thiohydan DIMERCAPTANS Test Results with Dispersion I Gms. Compound to Insolubilize Compound I Dispersion II lnsolubilization Chemical Solubi- Photosolubiliza- Containing 25 mg. Test A lization Test B tion Test 0 Silver Halide 1. 2,3-quinoxalinedithinl (L001 2. 2,3-dimercaptopropann1 0,0003 3. Toluene-,4- 0.0001 4. Glycol dhnei'eapto acetate. 0.004 5. CyclohexaneLl-dithiol- 0.001 6. 2,5-dimercapto-1,3,4-thiad o1 0.0001 7. 5,5-thiobis-(1,3,4-thiadiazole-2-thi0l)- 0. 0002 8. 3,5-dimercapto-4-cyano-1,2-thiq"n19 0 0015 9. N-cyano imine dlpotassium dithiolate 0. 04 10. 1,1-dicyano2,2-disorlium dithiolate ethylene... 0.02 11. 2-eyano-3,3-disodium dithiolate acrylamide.-. 02 12. 2-cyano-3,3-dipotassium dithiolate ethyl acrylate 0, 02 13. Cis-dicyanoethylene disodium thinlate 0.01 14. Trans-dicyano dithlolate ethylene ditetramcthylammonium salt.. 0. 01 15. 3, 5-disodiu1n dithiolate-4-cyano-l,2-tliio20le- 0, ()4

ARO MATIC MERCAPTANS Test Results with Dispersion I Grns. Compound to Insolubilize Compound Dispersion II Insolubihzatlon Chemical Solubil- Photosolubiliza- Containing 25 mg.

Test A izatron Test 13 tion Test C Silver llallde Thiophonol Insoluble Soluble Soluble 0. 00014 B-Naphtlrotlnol d d p-Chlorotbiophenol 2-nminotl1ioplrenol 4-aminotl1iopl1enol p-Brolnothio phenolp-Nitrothiophenol. t Thiosalicylic acid. o-Ioluenethiol rn-Tolucncthiol r.

p-Toluonethiol 4tbutylthiophenol 4-nonylthiophenol. 4-t-butyl-o-thiocresol ALIPIIATIC MERCAPTANS OR SULFIDES n-Propyl morcnptan Isopropyl mcrcaptan.

n-1$utyl nrereapmm Isobutyl incrcaptan See. butyl mercaptan. t-Butyl rnerenptan n-Amyl morcaptan lpcntanothiol Sec. nuiyl rnercoptan t-Amyl nieronptan n-llcxyl inercaptan n-l loptyl inorcnptnu 11-Octyl rnercaptnn t-Ootyl niorcaptom. .r 2-othyl-l-hox:u1othiol n-Nonyl n1crcoptnn n-Docyl morcnptnn. n- Undocyl inerc-opt-Jn r n-lJudocyl morcaptan. t-Dodecyl mere-amen." 21. licu'zyl merz'nptan .ZZ. ()-i\letl1ylbenzylmercaptr 2 3. p-Metbyl benzyl morcaptamt. O-Ethyl benzylmorcaptam l5. p-Ethyl benzyl mercaptzmn 20. p-llietliozybentiylmercaptan. r 27. Ethyl mercapto acetate s 2S. Morcnpto succinic acid." 29. Methyl mercapto acetater 30. Isooctyl tliioglycolate 31. Isooctyl 3-rnercaptopropionate..

Moreapto-bis-[othyl mercapto acetate] sulfide 33. Di-t-nonylpolysulildo 34. 'lliiobenzoic acid 35. leuereapto succinic acid 30. l-rlnoglycerol 3T. (Ethyl1nercapto)-acetic a Insoluble SELENIUM COMPOUNDS 1. Solenophcno] I soluble r. Soluble Soluble 0.0004 2. Selenourcn oluble NITROGEN CONTAINING COMPOUNDS ACTIVE AT HIGH pH 1, 'Z-mcthylbonzothiazole ethiodide oluble 0. 005 2. Z-hyrlrazinobenzothiawle. d (l l 0.03 3. E-aminobenzothiazole d 0.02 4. Q'aniinO-G-mcLhylbenzothiazolc. 0. 02 5. Z-ehlorobonzothiaaolm 0.015 G. 2-metl1ylt 1iazoliuc 0.04 7. s-nitrober .lrnidazo a. 0. 01 8. 3-rnethyl-i-(m-nitrophenyh-o p3 l to 0,03 9. 5-nitroinda'zole 0.01 10. Quinine bisulfite 0.03 11. Oetadeeyltrimethylammoniumchlori e. 0, 005 11 Carbazole ...d Insoluble 0.003

EXAMPLE VII sequently the fixed film was rinsed briefly in Water and A photographic element was prepared as described in bathed in a rapid acting fogging developer solution com- Exarnple 1. After drying, the element was bathed for 65 prising 1-phenyl-4-methyl-3-pyrazolidone and hydroquiabout 15 seconds in a solution of equal parts of water none as reducing agents to which there has been added and ethyl alcohol containing 5 grams of S-nitrobenzimidpotassium iodide. All of the above operations were carazolc and 20 grams of sodium hydroxide per liter. The ried out in ordinary fluorescent room illumination. Where dried element was then exposed behind a photographic a more sensitve product is prepared by appropriate selectransparency for 10 seconds to the radiation from a Gen- 70 tion of such factors as grain size, silver halide composieral Electric 2A photoflood lamp at a distance of about tion, etc., it is desirable to use conventional photographic 6 inches. The exposed element was then immersed in a dark room handling of the element prior to the image 0.5 M sodium hydroxide solution containing 64 grams of exposure. During the fixing step, the treated element is sodium thiosulfate per liter for /2 to 1 minute resulting converted into an exact reproduction (i,e., direct positive 1n removal of the silver salt 111 the exposed areas. Subsilver hallde image which 1s converted to a corresponding tion.

13 silver image in the second developing step) of the original transparency. After brief washing in water and drying, it is satisfactory for use in any application where an exact reproduction is desired, e.g., in the graphic arts field, for a projection transparency, etc.

No silver halide image is obtained when a similarly prepared and exposed sample is bathed in an acid rather than the highly alkaline sodium thiosulfate solution described above.

EXAMPLE VIII Example VII was repeated except that for the S-nitrobenzimidazole of that example a solution of S-nitroindazole of the same concentration was used to give similar results to those described in Example VII.

EXAMPLE IX Example VII was repeated except that Z-methylbenzothiazole ethiodide was substituted for the S-nitrobenzimidazole and a small quantity of potassium bromide was added to the aqueous alkaline sodium thiosulfate solu- The results were similar to those obtained in Example VII and VIII but the quality of the positive image was not as good.

EXAMPLE X Example VII was repeated except that 2-amino-6- methylbenzothiazole was substituted for the S-nitrobenzimidazole of that example. In this case either an acid or alkaline sodium thiosulfate solution gave results similar to Example IX.

EXAMPLE XI Example VII was repeated except that benzimidazole was substituted for the S-nitrobenzimidazole of that example. In this case no image was obtained since benzirnidazole did not insolubilize the silver halide.

Other experiments have shown that the insolubilization of silver halide by alkaline 5-nitrobenzimidazole may be enhanced by adding additional agents to the emulsion and/ or the sodium thiosulfate fixing solution. Substances which have proven eifective in this way are cyanine dyes, bromide ion, certain polyethylene glycols and mercaptans.

EXAMPLE XII An emulsion as described in Dispersion II, Example VI was redispersed in a 5% gelatin solution which contained 47 g. gelatin per mole of the silver halide. A pI-I 6.0i.1 was maintained Whiel dispersing min. at 110 F. The emulsion was brought to 2320 g. by addition of water and the temperature adjusted to 120 F. Four-tenths of a gram of MPT (Z-mercapto-4-phenylthiazole) was added per mole of silver halide from a 1% by weight ethanol solution. Chrome alum hardener was added and the emulsion was diluted with water to a total weight of 2334 g. per mole of silver halide. This emulsion was applied at a coating weight of 46 mg. of silver per square decimeter on 0.004 inch thick polyester photographic film base as described in Example I. The coating, after imagewise exposure, showed a greater rate of fixing in a 1.0 N (0.5 molar) aqueous sodium thiosulfate in exposed areas than in the unexposed areas so as to form a positive silver halide image. Subsequent flashing to white light, followed by treatment with a reducing agent (a conventional photographic developing solution containing 1- phenyl-4-methyl-3-pyrazolidone and hydroquinone), resulted in the formation of a positive image of metallic silver.

EXAMPLE XIII Example XII was repeated except that other mercaptan compounds, in the same amounts by weight, were examined in place of MPT. After photographic processing as described in Example XII, the optical densities of completely unexposed areas and heavily exposed areas of the film were determined using a Western Electric RA-ltlO-C Densitometer.

Compound Optical Density Unexposed Exposed Q-mereapto-erphenylthiazole 1. 0. 05 6-isobutrylamino-2-mereaptob enzothiazole 0. 45 0. 40 6-0ctanoylamino-2-mei'captobenzothiazole 1. 24 1. 20 G-isobutrylam mo-2-mercaptobenzothiaz0l e. 0. 84 0. 80 p-Brornothiophenol 0. 29 0. 15 4-phenylmereaptotetrazole 0. 21 0. 15 Phenylbiguanidemercaptobenzothiazole. 1. 24 1. 20 Dodomnorhiol 0. 21 0.10 Dibenzylthiourea 0. 79 0. 70 Mereaptouu deconic acid- 1. 20 1. 1O Z-morcaptob enzothiazole. 2. 73 0. 40 hiercaptobenzoxa zole 0. 56 0. 38 1,3-dibenzylthiourea 0. 85 0. 24

EXAMPLE XIV Optical Density Weight of MP1 Unexposed Heavily Exposed 1.25 gjmole of silver 2.00 0. 15 2.50 gJmole of silver. 2.10 0.14 3.75 g./mole of silver 2.18 0.15 5.00 g./m0le ofsilver 1. 0.13

EXAMPLE XV A silver bromide emulsion was prepared by adding one mole of 1.5 N AgNO to 1.2 moles of a solution of 0.7 N KBr containing 33 g. of gelatin. After ripening 10 minutes at 130 F. the emulsion was coagulated by the addition of a 12% aqueous solution of a water-soluble, acid-soluble partial acetal of polyvinyl alcohol and o-sulfobenzaldehyde and consisting of 5 g. of suifonate surfur per g. of polymer, followed by the addition of sulfuric acid to lower the pH to 2.6. An aqueous solution containing 7.2 g. of KBr was then added and the curds were redispersed at 95 F. for 10 minutes with high shear stirring. Sodium hydroxide was added to adjust the pH to 4.1 and redispersion was continued for 30 minutes. The curds were then dispersed in an aqueous 16% by weight gelatin solution to give a total of 300 g. gelatin per mole of silver bromide. Then 2-mercapto-4- phenylthiazole was added from a 1% ethanol solution to give a total of 0.6 g. per mole of silver bromide. The emulsion was adjusted to 2700 g. with water after addition of a chrome alum hardening agent. The emulsion was applied at a coating weight of 35 mg. of silver per square decimeter. The coating showed more rapid fixing in an exposed area than in an unexposed area such that upon intensification by subsequent re-exposure and chemical development as in Example XII a positive metallic silver image was attained with a maximum optical density of 1.26 and a minimum optical density of 0.35.

EXAMPLE XVI A silver chloride emulsion was prepared in the same manner as in Example XV except KCl was used instead of KBr at precipitation and redispersion. The KCl at precipitation was present in an amount of 1.08 moles per mole of silver nitrate. The curds were dispersed in 17% gelatin to give a total of 94 g. gelatin per mole of silver bromide. MPT (Z-mercapto 4 phenylthiazole) was added from a 1% ethanol solution to give a total of 1.0 g. per mole of silver chloride. The emulsion was adjusted to a final weight of 1950 g. with water after the addition of chrome alum as a hardening agent. The

15 emulsion was applied at a coating weight of 35 mg. of silver per square decimeter. The coating showed more rapid fixing in an exposed area such that upon intensification by subsequent re-exposnre and chemical development as in Example XII a positive metallic silver image was attained with maximum and minimum optical densities of 1.21 and 0.18.

EXAMPLE XVII A silver bromoiodide emulsion of the medical X-ray type was prepared by adding ammonia converted silver nitrate to a mixture of ammonium bromide and potassium iodide in gelatin. After ripening, the emulsion was coagulation washed. The final emulsion contained 1.6 mole percent silver iodide and 98.4 mole percent silver bromide. The washed curds were redispersed in gelatin to give a total of 200 g. of gelatin per mole of silver halide. To this emulsion there was added 1.3 g. of Z-mercapto- 4-phenylthiazole per mole of silver halide and the emulsion was applied to the support described in Example. I at a coating weight of 35 mg. of silver per sq. dec. The coated material showed more rapid fixing in an exposed than in an unexposed area such that upon intensification by subsequent re-exposure and chemical development as in Example XII a positive metallic silver image was attained with maximum and minimum optical densities of 0.91 and 0.50.

EXAMPLE XVIII From an alkaline solution, S-nitrobenzimidazole was added to an emulsion similar to that of Example XII at 2.7 g. per mole of silver halide. This emulsion, with a pH raised to 10.6 by the above addition, was coated as in Example XII, dried and given an imagewise exposure to white light. The exposed coating was then treated with an aqueous sodium thiosulfate solution which was 1.5 N in sodium hydroxide to yield a positive silver halide image. The image was intensified by flashing with white light followed by chemical reduction to a metallic silver image as described in Example XII.

EXAMPLE XIX A photographic layer was made by evaporating silver chloride onto the film base described in Example I, using a High Vacuum Evaporator, Model No. SC3 (Optical Film Engineering Co.). The vacuum apparatus employed a tantalum ribbon and operated at a pressure of 3 l0 microns of mercury. Using about 280 milligrams of AgCl at a distance of 24 cm. from the film base, a coating weight of AgCl of about 4 mg/dm. was obtained.

The vacuum-coated film was bathed for 15 sec. in the ethanol-water (25/10) solution of 2-mercapto-4-phenylthiazole of Example I, dried and exposed stepwise for 5, 10, 20, 40 and 80 seconds to a photofiood lamp (General Electric 2-A) at a distance of 6 inches. The exposed element was then immersed in 12.8% aqueous sodium thiosulfate for 30 seconds, rinsed in water for 10 seconds and then bathed in a developer solution as described in Example I.

A direct-positive image was formed by the and 40-second exposures, i.e., imagewise density decreased with increasing exposure. However, when the exposure was increased to 80 seconds, a negative image was formed, the system reversing or solarizing by increased exposure like conventional silver halide systems.

EXAMPLE XX Example V was essentially repeated except that (a) the element was bathed for 60 seconds (rather than seconds) in the solution of Z-mercapto-4-phenylthiazole, (b) the sodium thiosulfate fixing solution was replaced with an aqueous solution containing, on a liter basis, 150 g. KCNS and 50 ml. of 1 molar Na CO and the time was extended to 2 minutes and (c) safe lights were used throughout all operations up to the 60 second treatment with developer solution, with ordinary fiuorosecent i6 room illumination being used subsequently. A direct positive image was formed, similar to that of Example V.

EXAMPLE XXI A photosoluble element was prepared from a conventional orthoehromatic fully sensitized lithographic gelatino silver halide film (comprising 70 mole percent silver chloride and 30 mole percent silver bromide) having a coating weight of about milligrams per square decimeter silver halide. The film support was the same as that described in Example I. Under safe light conditions, this film was bathed for 30 seconds in the dilute ethanol-water solution of 2n1ercapto-4-phenylthiazole described in Example I. The dried element was exposed behind a square-root-oftwo photographic step wedge for 10 seconds to the radiation from a General Electric Z-A photofiood lamp, operating at 115 volts and at a distance of 6 inches. The exposed element was then immersed in a 12.8% aqueous solution of sodium thiosullate for seconds resulting in remova1 of the silver salt in the exposed areas. The fixed fL m was subsequently rinsed briefly in Water and then, under white room lights, bathed in a rapid acting photographic developer comprising l-phenyl-4-methyl-3pyrazolidone and hydroquinone as reducing agents. A direct positive stepwise silver image formed.

Another sample of the photosoluble element (bathed in the above solution of 2-mercapto-4-phenylthiazole) was exposed behind a square-root-of-two step wedge for 3 seconds to the radiation from the above described photoi'lood lamp operating at 25 volts and at a distance of 2 feet.

The exposed element was then developed for 2 minutes at 68 F, in the following conventional photographic developer:

G. Monomethyl-p-aminophenolsulfate 3.0 Hydroquinone 9.0 N21 SO anhydrous 50.0 K CC= 50.0 KBr 4.5

Water to make 1 liter.

The film element was then rinsed 15 seconds in running Water at 68 F., fixed 5 minutes at 68 F. in a potassium alum sodium thiosulfate fixing bath (the film required two minutes to clear and dried to give a slow and very weal; negative silver image) (Negative Image I).

Another sample of the ortho-sensitized litho film (which did not receive the treatment with 2-mercapt0-4-phenylthiazole) was exposed, developed, fixed and washed in exactly the same way as just described to give a high speed high density negative image (Negative Image II). In this instance, the film required only 20 seconds in the fixing bath to clear. The optical densities resulting from the positive and two negative images are given below:

Total Silver Density Exposure Step No. Positive Negative Negative Image Image I Image 11 3. 14 0t 3. 2t 2. l7 08 4. 0+ 1. 03 19 4. 0+ 20 47 4. 0+ 17 l. 12 1. (H-

The silver halide photosoluble elements used in accordance with this invention constitute the subject matter of my prior application Ser. No. 158,132 filed December 8, 1961 (abandoned January 21, 1963), and my related applications Ser. No. 236,412 and Ser. N0. 236,418, filed on even date herewith, that are continuations-in-part of said prior application. They differ from conventional silver halide emulsions containing antifogging agents in that the insolubilizing compounds used in the photosoluble elements are present in substantially greater than fog inhibiting amounts, such amounts are the maximum quantity of material which provides low fog without serious loss in speed and photographic quality. For this reason it is not practical to use photosoluble elements in place of ordinary silver halide photographic materials. When photosoluble elements are exposed and processed normally, development proceeds slowly and incompletely to give a negative silver image having much less speed and lower density. In addition, fixing is slower and may be incomplete for practical fixing times. Thus photosoluble elements require longer conventional processing times and give slower speed, inferior quality images when compared to ordinary silver halide photographic elements.

The photographic processes of the invention have advantages over previously known systems based on selective reduction of exposed silver halide for forming either direct positive or negative images without resorting to the special effects and sensitizing procedures previously used for preparing such images. In addition, since image formation does not require selective reduction, this present process is not limited to the use of certain photographic developing agents but may be accomplished by using a Wide range of reducing agents. Many such compounds are of very low cost and can be used to form images of much higher covering power than customary, thus effecting important economies in processing, as well as greatly increasing the efficiency of the silver image with a resultant increase in sensitivity.

Another advantage of this invention is that it provides a process for forming silver images that do not require special equipment but instead can be used with conventional equipment and apparatus. A further advantage is that the processes can be carried out successively by photographic technicans and photographers of ordinary skill with, in many instances, the exposing and processing steps being carried out under ordinary room light conditions. A still further advantage is that the processes utilize conventional reducing agents, e.g., developers and fixing agents. Still additional advantages will be apparent from the above description of the invention.

This application is a continuation-in-part of my application Ser. No. 158,132, filed December 8, 1961, for Photographic Compositions and Processes (abandoned).

I claim:

1. A process which comprises, in the order stated, the

' sequential steps of:

(a) exposing, imagewise, to actinic radiation, a photographic element containing silver halide crystals made relatively less soluble in a silver halide solvent by treatment with an organic compound capable of forming a silver salt and whose silver salt is of lower solubility in water than silver chloride, and

(b) prior to any reducing step treating said element with an aqueous solution of a silver halide solvent, thereby effecting solubilization of the silver halide in the more exposed areas at a rate substantially greater than in the less exposed areas until a positive image comprised of silver halide is produced;

said organic compound being present in such an amount, in terms of the ratio of its weight to the surface area of the silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide dispersion, 70/30 mole percent, gelatin emulsion containing 0.29 mg. of Ag in one-half ml., and said silver chlorobromide dispersion is treated with 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag and 100 mg. or" sodium thiosulfate, at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with %by weight aqueous 18 sodium hypochlorite and 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag, 25 mg. of sodium hypochlorite and mg. of sodium thiosulfate, after vigorous agitation of both dispersions for 30 seconds at 25 C.

2. A process according to claim 1 wherein said solvent is an alkali metal thiosulfate.

3. A process according to claim 1 wherein said solvent is sodium thiosulfa'te.

4. A process according to claim 1 wherein said silver halide crystals are silver chlorobromide crystals.

5. A process according to claim 1 wherein said actinic radiation is in the visible region of the spectrum.

6. A process according to claim 1 wherein the less soluble silver halide crystals constitute the sole constituent of the image forming layer of the element.

7. A process for the formation of photographic images comprising (a) exposing, imagewise, to actinic radiation a photographic element comprising, in the order stated, the sequential steps of a layer of a water-permeable organic colloid containing silver halide crystals rendered relatively less soluble in a silver halide solvent by treatment with an organic compound capable of forming a silver salt and whose silver salt is of lower solubility in water than silver chloride, and

(b) prior to any reducing step treating said element with an aqueous solution of a silver halide solvent, thereby effecting solubilization of the silver halide in the more exposed areas at a rate substantially greater than in the less exposed areas until a positive image comprised of silver halide is produced;

said organic compound being present in such an amount, in terms of the ratio of its weight to the surface area of the silver halide crystals,

that when admixed in such ratio with an aqueous silver chlorobromide dispersion, 70/30 mole percent, gelatin emulsion containing 0.29 mg. of Ag in one-half ml., and said silver chlorobromide dispersion is treated with 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag and 100 mg. of sodium thiosulfate, at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with 5% by weight aqueous sodium hypochlorite and 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag, 25 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate, after vigorous agitation of both dispersions for 30 seconds at 25 C. 8. A process according to claim 7 wherein said solvent is an alkali metal thiosulfate.

9. A process according to claim 7 wherein said solvent is sodium thiosulfate.

10. A process according to claim 7 wherein said silver halide crystals are silver chlorobromide crystals.

11. A process according to claim 7 wherein said actinic radiation is in the visible region of the spectrum.

12. A process according to claim 7 wherein said organic compound in at least one form is represented by the formula where R is an organic radical having a carbon atom linked directly to S.

13. A process according to claim 7 wherein said colloid is gelatin.

14. A process for the formation of direct positive images which comprises, in the order stated, the sequential steps of: I

(a) exposing, imagewise, to actinic radiation, a photographic element containing silver halide crystalsren- 3,155,507 19 20 dered relatively less soluble in a silver halide solvent images which comprises, in the order stated, the sequential by treatment with an organic compound capable of steps of:

forming a silver salt and whose silver salt is of lower (a) exposing, imagewise, to actinic radiation, a photosolubility in water than silver chloride. graphic element containing silver halide crystals ren- (b) prior to any reducing step treating said element dered relatively less soluble in a silver halide solvent with an aqueous solution of a silver halide solvent, by treatment with an organic compound capable of thereby efiecting solubilization of the silver halide in forming a silver salt and whose silver salt is of lower the more exposed areas at a rate substantially greater solubility in water than silver chloride, than in the less exposed areas until a positive image (b) prior to any reducing step treating the entire sureomprised of silver halide is produced; face of said element with an aqueous solution of said organic compound being present in such an a silver halide solvent, thereby effecting solubilizaamount, in terms of the ratio of its weight to tion of the silver halide in the more exposed areas the surface area of the silver halide crystals, at a rate substantially greater than in the less exposed that when admixed in such ratio with an aqueous areas until a positive image comprised of silver silver chlorobromide dispersion, 70/30 mole perhalide is produced, cent, gelatin emulsion containing 0.29 mg. of said organic compound being present in such an Ag in one-half mL, and said silver chlorobromide amount, in terms of the ratio of its weight to the dispersion is treated with 10% by weight surface area of the silver halide crystals, that aqueous sodium thiosulfate, so that the resulting when admixed in such ratio with an aqueous mixture contains 0.29 mg. of Ag and 100 mg. silver chlorobromide dispersion, 70/30 mole perof sodium thiosulfate, at least three times the cent, gelatin emulsion containing 0.29 mg. of amount of silver chlorobromide remains undis- Ag in one-half ml., and said silver chlorobromide solved as compared with a similar dispersion dispersion is treated with 10% by weight successively treated with 5% by weight aqueous aqueous sodium thiosulfate, so that the resultsodium hypochlorite and 10% by weight aqueous ing mixture contains 0.29 mg. of Ag and 100 sodium thiosulfate, so that the resulting mixmg. of sodium thiosulfate, at least three times ture contains 0.29 mg. of Ag, 25 mg. of sodium the amount of silver clilorobromide remains unhypochlorite and 100 mg. of sodium thiosulfate, dissolved as compared with a similar dispersion after vigorous agitation of both dispersions for successively treated with 5% by weight aqueous seconds at 25 C. 30 sodium hypochlorite and 10% by weight aque- (c) washing the element with Water. ous sodium thiosulfate, so that the resulting mix- 15. A process according to claim 14 wherein said ture contains 0.29 mg. of Ag, 25 mg. of sodium organic compound is a mercaptothiazole. hypochlorite and 100 mg. of sodium thiosulfate,

16. A process according to claim 14 wherein said after vigorous agitation of both dispersions for organic compound is a 2-mercapto-4-pl1enylthiazole. 30 seconds at 25 C.,

(c) washing the resulting layers with water, and

17. A process for the formation of direct positive (d) converting the residual silver halide to silver by images which comprises, in the order stated, the sequential steps of: treating it in an aqueous fogging developer solution.

(a) exposing, imagewise, to actinic radiation, a photo- 19. A process for the formation of direct positive graphic element containing silver halide crystals renimages which comprises, in the order stated, the sequential dered relatively less soluble in a silver halide solvent steps of;

y treatment with all 0rgahi Compound Capable of (a) exposing, imagewise, to actinic radiation, a photoforming a silver salt and whose silver salt is of lower solubility in water than silver chloride,

graphic element containing silver halide crystals rendered relatively less soluble in a silver halide solvent Prior to y reducing p treating the entire by treatment with an organic compound capable of face of Said element with an aq eous Solution f forming a silver salt and whose silver salt is of lower a silver halide solvent, thereby effecting solubilizasolubility in water than silver chloride, tion of the silver halide in the more exposed areas (b) prior to any reducing step treating the entire suratarate substantially greater than in the less exposed fa of said element with an aqueous solution of areas until a positive image comprised of silver a silver halide solvent, thereby effecting solubilizahalide is produced, tion of the silver halide in the more exposed areas Said Organic Compound hfiihg Present in Such an at a rate substantially greater than in the less exposed amount, in terms of the ratio of its weight to areas until a positive image comprised of silver the surface area of the silver halide crystals, halide is produced, that when admixed in such ratio with an aqueous said organic compound being present in such an silver chlorobrornide dispersion, 70/30 mole peramount, in terms of the ratio of its Weight to the cent, gelatin emulsion containing 0.29 mg. of surface area of the silver halide crystals, that Aginone-half ml., and said silver chlorobromide when admixed h h with an aqueous dispersion is treated with 10% by weight silver chlorobromide d1spers1on, 70/30 mole peraqueous sodium thiosulfate, so that the resulting ge atin emulsion containing 0.29 mg, of mixture contains 0.29 mg. of Ag and 100 mg. Ag in one-half ml., and said silver chlorobrornide of sodium thiosulfate, at least three times the dlsperslon treaied Wlth 10% by welght amount of silver chlorobromide remains undisliqueolls Sodlum flilosulfate so that the resultsolved as compared with a similar dispersion mg contains of g a I 5 mg. of sodium thiosulfate, at least three times Suc9"SS1ve1y treatefl Wnh 5% by Weight aqleous the amount of silver chlorobromide remains unsodlum hylfochbme and 10% by l q dissolved as compared with a similar dispersion sodlum tkllosulfate that the resulting l successively treated with 5% by weight aqueous ture contafns of Sodmm sodium hypochlorite and 10% by weight aquehypochlome and 100 mg of sodlum thmsulfate, ous sodium thiosulfate, so that the resulting mixflfief Vigorous agitation of both dispersions ture contains 0.29 mg. of Ag, 25 mg. of sodium 30 Seconds hypochlorite and mg. of sodium thiosulfate,

( Washing the resulting layfifs With Water, and after vigorous agitation of both dispersions for (d) intensifying the silver halide image. 30 seconds at 25 C.,

18. A process for the formation of direct positive 7 (c) washing the resulting layers with water,

3,155,507 21 (d) converting the residual silver halide to silver by treating it in an aqueous fogging developer solution,

successively treated with by weight aqueous sodium hypochlorite and by weight aqueand ous sodium thiosulfate, so that the resulting mix- (e) washing the developed layer to reveal a positive ture contains 0.29 mg. of Ag, 25 mg. of sodium silver image in the original non-exposed areas. 5 hypochlorite and 100 mg. of sodium thiosulfate,

20. A process for the formation of photographic images comprising, in the order stated, the sequential steps of:

(a) exposing, imagewise, to actinic radiation, a photoafter vigorous agitation of both dispersions for 30 seconds at 25 C., (c) washing the resulting layers with water, and

graphic element comprising a layer of a waterpermeable organic colloid containing silver halide crystals rendered relatively les soluble in a silver halide solvent by treatment with an organic compound capable of forming a silver salt and whose silver salt is of lower solubility in water than silver chloride,

(b) prior to any reducing step treating the entire surface of said element with an aqueous solution of a silver halide solvent, thereby elfecting solubilization of the silver halide in the more exposed areas at a rate substantially greater than in the less exposed areas until a positive image comprised of silver halide is produced,

said organic compound being present in such an amount, in terms of the ratio of its weight to the surface area of the silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide dispersion, 70/30 mole percent, gelatin emulsion containing 0.29 mg. of Ag in one-half ml., and said silver chlorobromide dispersion is treated with 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag and 100 mg. of sodium 'thiosulfate, at least three times the amount of silver chlorobrornide remains undissolved as compared with a similar dispersion (d) converting the residual silver halide to silver by 10 treating it in an aqueous fogging developer solution. 21. A process according to claim 20 wherein said colloid is gelatin and said solvent is sodium thiosulfate.

References Cited in the file of this patent UNITED STATES PATENTS 2,214,446 Albers et a1 Sept. 10, 1940 2,710,256 Ecklcr et a1 June 7, 1955 3,008,829 Clementi et a1 Nov. 14, 1961 3,038,800 Luckey et al June 12, 1962 3,046,130 Dersch et al July 24, 1962 3,063,837 Lassig et al Nov. 13, 1962 3,080,230 Haydn et al Mar. 5, 1963 FOREIGN PATENTS 724,001 Great Britain Feb. 16, 1952 OTHER REFERENCES Land: A New One-Step Photographic Process, Journal of the Optical Society of America, vol. 37, No. 2, pp. 61-77, February 1947.

Keelan: The Journal of Photographic Science, vol. 5, November/December 1957, pp. 144 and 145.

Faerman et a1.: Chemical Abst., vol. 52, No. 2, column 937d, January 25, 1958 (abstract of Otdel Chim, Nauk, 5, 107-13 (1957).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3, 155 507 November 3, 1964 Ralph Kingsley Blake It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l4, line 20, for "amount" read amounts column 18, lines 21 and 22, strike out in the order stated,

the sequential steps of" and insert the same after "comprising" in line 19, same column 18.

Signed and sealed this lstday of June 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attcsting Officer Commissioner of Patents 

1. A PROCESS WHICH COMPRISES, IN THE ORDER STATED, THE SEQUENTIAL STEPS OF: (A) EXPOSING, IMAGEWISE, TO ACTINIC RADIATION, A PHOTOGRAPHIC ELEMENT CONTAINING SILVER HALIDE CRYSTALS MADE RELATIVELY LESS SOLUBLE IN A SILVER HALIDE SOLVENT BY TREATMENT WITH AN ORGANIC COMPOUND CAPABLE OF FORMING A SILVER SALT AND WHOSE SILVER SALT IS OF LOWER SOLUBILITY IN WATER THAN SILVER CHLORIDE, AND (B) PRIOR TO ANY REDUCING STEP TREATING SAID ELEMENT WITH AN AQUEOUS SOLUTION OF A SILVER HALIDE SOLVENT, THEREBY EFFECTING SOLUBILIZATION OF THE SILVER HALIDE IN THE MORE EXPOSED AREAS AT A RATE SUBSTANTIALLY GREATER THAN IN THE LESS EXPOSED AREAS UNTIL A POSITIVE IMAGE COMPRISED OF SILVER HALIDE IS PRODUCED; SAID ORGANIC COMPOUND BEING PRESENT IN SUCH AN AMOUNT, IN TERMS OF THE RATIO OF ITS WEIGHT TO THE SURFACE AREA OF THE SILVER HALIDE CRYSTALS, THAT WHEN ADMIXED IN SUCH RATIO WITH AN AQUEOUS SILVER CHLOROBROMIDE DISPERSION, 70/30 MOLE PERCENT, GELATIN EMULSION CONTAINING 0.29 MG. OF AG IN ONE-HALF ML., AND SAID SILVER CHLOROBROMIDE DISPERSION IS TREATED WITH 10% BY WEIGHT AQUEOUS SODIUM THIOSULFATE, SO THAT THE RESULTING MIXTURE CONTAINS 0.29 MG. OF AG AND 100 MG. OF SODIUM THIOSULFATE, AT LEAST THREE TIMES THE AMOUNT OF SILVER CHLOROBROMIDE REMAINS UNDISSOLVED AS COMPARED WITH A SIMILAR DISPERSION SUCCESSIVELY TREATED WITH 5% BY WEIGHT AQUEOUS SODIUM HYPOCHLORITE AND 10% BY WEIGHT AQUEOUS SODIUM THIOSULFATE, SO THAT THE RESULTING MIXTURE CONTAINS 0.29 MG. OF AG, 25 MG. OF SODIUM HYPOCHLORITEAND 100 MG. OF SODIUM THIOSULFATE, AFTER VIGOROUS AGITATION OF BOTH DISPERSIONS FOR 30 SECONDS AT 25*C. 